Recoilless firearm



July 13, w48. c. w. mussen RECOILLESS FIREARM 3 Sheets-Sheet 2 FiledNov.

QvwMvbO/b WALTDN Musea@ July 13, 1948. c.\w. MUssER RECOILLESS FIREARM 3Sheets-Sheet 3 Filed Nov. 14, 1945 WSS Ot Ohh mm HM mhtvl bzw En@ unwwmi 92E@ gmc/vwo@ EAALTDN Muss-ER lntented July 13 1948 RECOILLESSFIREARM Clarence Walton Musser, Philadelphia, Pa., as-

signer to the United States oi America as represented by the Secretaryol' War (Granted under the act of March 3, 1883, as

amendedv April 30, 1928; 370 0. G. 757) 7 Claims.

The invention described herein may be manufactured and used by or forthe Government for governmental purposes, without the payment to me ofany royalty thereon.

My invention relates to firearms of the recoilless type and it hasspecial reference lto nonrecoil guns wherein the forces of rearwardreaction that result from projectile disch-arge are neutralized byforwardly acting counter forces simultaneously set up by a rearwardescape of propellant powder gas through openings or orifices in the gunsbreech.

Broadly stated, the object of my invention is to improve the design andextend the usefulness of recoilless guns which incorporate principles ofconstruction and operation earlier disclosed and claimed by co-pendingapplications of Krueger- Musser: (a) Serial No. 536,590, filed May 20,1944, for Reooiiless firearms, ammunition therefor, and ballistic designthereof"; and (b) Serial No. ??,830, led February 14, 1945, forRecoilless rearm and ammunition therefor."

A more specii'lc object is to substantially increase the eective life ofsuch guns over that possessed by their forerunners in the recoilless gunfield.

Another object is to provide non-recoil Sun constructions which arepeculiarly adapted to iirearms of 75 millimeter and other high calibersand which eliminate the problem of recoil adiustment that characterizesprior art recoilless weapons.

n further object is to protect the guns extractor mechanism from erosionby the blast of escaping gases.

A still further object is to attain the foregoing improvements withoutsacrificing the advantages oi light weight. ruggedness and simplicity ofaction.

Other objects and advantages will become apparent as -the disclosure anddescription hereof proceeds.

In practicing my invention I accomplish the foregoing aims by utilizingthe "annular breech orifice," the "perforated cartridge case, and the"specially tapered gun chamber" principles which copending applicationsSer. Nos. V536,59() and 577,830 broadly cover. In supplement thereto Ihave provided a unique gun chamber reliner which makes the replacementof gun parts subject to erosive wear caused by rearwardly expelled gasesa comparatively simple and rapid operation.

As is later brought out this reliner may be of a uniform design forlarge and small weapons. Regardless of the weapons caliber, only onesize reliner is necessary throughout the life of the gun. Instead ofadjusting differently dimen'sioned recoil adjusting devices when wearoccurs, as in the prior art, a gun may be completely renewed byreplacement of the worn reliner.

My new weapon design additionally shields the cartridge case extractorfrom corrosive powder gases and causes .the extractor further toautomatically lock the breech in the "open position.

My invention together with illustrative embodiments .thereof will bestbe understood from the following description when taken in conjunctionwith the accompanying drawings wherein:

Fig. 1 is a rear view showing of my improvements applied to a recoillessgun of mm. caliber;

Fig. 2 presents a showing, in partial section from line 2-2 of Fig. 1,of the chamber, breech, chamber reliner, extractor, hinge mounting andriiled barrel;

Fig. 3 is a section on line 3-3 of Fig. 1 through opposing Venturi-likeopenings that extend axially through the chamber reliner;

Fig. 4 shows my weapon in rear elevation with the breech bar and breechblock thereof rotated to the unlatohed position;

Fig. 5 is a section on line 5--5 of Fig. 4 showing how the extractor isreleased from rotational locking engagement with the breech block whenthe breech is closed;

Fig. 5A is a similar view showing .the breech partially opened andillustrating the extractor partially entered under spring pressure intolocking engagement with the breech block;

Fig. 5B indicates how the extractor positively locks the breech blockagainst rotative movement when the block is further withdrawn from thechamber; and

Fig. 6 is a graph showing how the firing lifetime of my new gun has beenextended far beyond that of its comparable prior art recoilless firearm.

Problem to be solved My invention comprises improvements in recoillessrearms of the open breech type described and shown in the co-pendingapplications of Kroeger-Musser, Serial Nos. 536,590 and 577,830, earlieridentified. The weapons of those earlier applications have alreadygained widespread acclaim due to their exceptional eectiveness andmilitary value on battleelds around the world; they have, in fact, madeeach infantryman a. potential artilleryman with concomitant accuracyapproaching that of a sharpshooter rifleman.

When those earlier weapons were originally designed, the broad objectswere to provide the first successful-recollless guns having theabovedescribed effectiveness. Such aims were accomplished by thosefirearms. Since then, the principal objectives have been Ito increasethe firing lifetime and reduce the time and effort necessary to maintainthe gun in satisfactory firing condition.

' Experience with the above-mentioned early recollless firearm designshave shown that a maximum of about 450 rounds is the average lifetime ofthe 75 mm. construction shown by Ser. 577,830 depending on the type ofpropellant powder used. To attain even this figure it is necessary toutilize about six changes of a recoil adjusting ring or cone (54 of Ser.577,8305 drawings) which is subject to erosion from .the blast ofrearwardly escaping explosive gases. Moreover, the proper selection andreplacement of this ring requires a certain amount of skill, time andtraining which are additional disadvantages when such changes have to bemade under combat conditions.

Elimination of the foregoing problem has been accomplished by a uniqueshaping of the venturis through which the .rearwardly moving gasesescape, and a novel arrangement for renewing gaseously eroded gun partswith but a minimum of time and skill. In addition this new constructionincludes means for protecting the extractor mechanism from rapid gaseouserosion, thereby eliminating another part-renewal problem.

Advantages of new gun over prior art The aforementioned handicaps in theprior art have been, for all practical purposes, overcome by my heredisclosed improvements which have enabled such guns to far outlast theirforerunners in the recollless weapon field.

For example, it has been folmd that the same number of ammunition rounds(about 450, depending on the powder used) may be red from my improvedfirearm before the novel reliner requires replacement as could be shotfrom the earlier type rifle during the latter's entire lifetime. Sincemany new reliners may be substituted before other parts of the gun areworn to the point where the entire weapon is unusable, it may readily beseen th'at the life span of the new recoilless gun has been tremendouslyexpanded.

Reference to Fig. 6 will graphically illustrate these advantages. Thatdrawing plots the total firing life of the gun against the attainablevelocity (or range) of the projectiles fired therefrom, showing the rateof change in velocity (or range) which occurs when the guns recoiladjusting ring (54 of Ser. No. 577,8305 drawings) or unique chamberreliner I3 is worn by erosion from its "new gun condition to a pointwhere excessive correction factors must be used. The intermediate stagesrefer to proportionate levels of firing utility.

Th'e abscissae are plotted along the ring lifetime of the illustrated 75mm. gun and its earlier counterpart described in Ser. No. 577,830showing clearly the relative life of the two weapons. The markedabscissa points 1.46 to 1.58 represent increasing sizes ofrecoil-adjusting replaceable rings or cones (54 of Ser. 577,830sdrawings) which need to be installed in the earlier Kroeger-Musserweapon throughout its firing lifetime as erosion enlarges the gunsannular orifice or throat.

The represented curves in Fig. 6 compare the longevity and etllciency ofmy improved weapon described h'erein with the older type recolllessrifle.- The dotted-line curve showsthe 'lowering in velocity whichresults from enlargement of the prior art guns annular orifice due -toerosion of the aforementioned rings andthe gun chamber wall. As more andmore 1rounds are fired from a rearm whose original recoil adjusting ringis of the size exemplified by 1.46 in Fig. 6, velocity changes from theaforementioned new gun condition to the minimum permissible velocitynecessary for useful operation.

This course is repeated through successive ring changes (first 1.48,then 1.50, etc.), each time replacing the worn adjusting member with oneof next larger size. The larger rings each reduce the throat areatherearound by an amount suiiicient to restore the originalbcre-to-throat ratio, simultaneously reestablishing velocity at themaximum or new gun level. As sh'own, the described velocity or gunsrange renewal can be effected by such ring changes about six times inthe life of the prior art weapon before wear of its chamber requiresthat it be discarded.

With my improvement, changes in velocity are far more gradual, as thesolid-line curve of Fig. 6 indicates. This accounts for the earliermentioned fact that approximately the same number of projectiles (about450 rounds) can be fired before the unique chamber reliner needsreplacement, as formerly could be shot in the entire sixfold-renewedlifetime of the prior art recollless firearm.

Replacement of the novel chamber reliner completely renews the'gun forall practical purposes so that the just stated firing record may beduplicated. This renovation maybe repeated over and over again, as allparts subject to any appreciable wear are thus supplanted by new ones.The Fig. 6 graph thus indicates an "unlimited ring lifetime for myimproved weapon. This is a theoretical possibility; and no attempt hasthus far been made to determine the actual gun life because of the vastamount of ammunition round and chamber reliners which would have to beexpended. Sufficient experimentation has, however, already beenperformed to prove that my hereinafter described improved recolllessrearm far outlasts its predecssors in the art.

The gun chamber "reliner of my invention The drawings vhereofillustratively show a recollless firearm having a chamber Ii whoserearward end is a cylldrical portion which is continuous with a forwardtapered portion that is threadably joined with a ried barrel I2. Thisfirearm construction is similar to that of the 75 mm. weapon shown inoo-pending application Serial No. 577,830. For convenience of reference,mention hereinafter will be made to the tapered" chamber Il; it shouldbe understood, however, that the chamber thus referred to is notentirely tapered, but preferably is constructed of a cylindrical portionand a tapered portion as just described and as shown by the drawings. Inaccordance with any invention, a removable ringshaped reliner i3 isthreadably attached at Il within the rear or breech end of gun chamberil, and there immovably secured by a stud 31 which is screwed through ablock 36,' the chamber li and into the reliner i3'as shown in Figs 2-5-5A-5B. The axial length of threaded juncture I4 is great enough toprovide a gas-tight seal without sasketing,

This new reliner It is provided with an essentially annular orice il(see Figs. 1-3-4) whose purpose is to control the iiow of rearwardly escaping powder gases so as to achieve zero recoil by utilizing theVenturi operative principles described in the co-pending applicationmentioned above. The shape of that orifice I5 has, however, beenredesigned and improved as will be more fully'brought out. v

In addition, my new reliner is designed to accommodate and shield fromgaseous erosion the guns case extractor fixture I9. This extractorfixture takes the form of a right-angled piece of metal, one entire armof which is anchored for limited movement within a slot 24 situated onthe forwardly facing surface of the breech blocks hinged supportingmember 23 as shown in Figs. 2-5-5A-5B. (By forwardly facing surface" ismeant that face which looks to the muzzle of the gun when the breechblock 20 is inserted into the closed-breech position of Fig. 2 or Fig.V5.)* The other extractor arm, which terminates in a hook il) (see Figs.5-5A-5B), protrudes resiliently (by virtue of the supporting spring Mtherefor) from the forwardly facing surface of supporting member 23.When the breech block is in the closed breech position this protrudingextractor arm matingly enters a recess IB (see Figs. 2 and 5) providedtherefor in reliner I3.

This extractor I@ facilitates case extraction and also serves to preventrotation of the guns breech block 2o when that block is in the openbreech position of Figs. 5A-5B, as will later be explained.

The ring-shaped reliner I 3 has a forward opening (fillable by thecartridge case 2d as showii) and an expanded rearward opening whoseinner periphery is threaded for engaging the lugs of the guns breechblock 2b.

Preservation of the size of the annular orifice (or venturi) it, isessential to the efcient operation of recoilless weapons of the openbreech type. Even though my improved design provides a shape whichminimizes erosion caused by the explosive gases, inevitable wear willrequire restoration of the original dimensions of those orifices inaccordance with the guns ballistic design, This may be readily achievedby replacement of the reliner it.

Such replacement is readily accomplished by removing screw di, then withthe breech block 2W in the open position shown in Fig. 5B, turning thereliner i3 counterciockwise out of its threadable engagement it with thegun chamber il; and reversing the procedure to insert the new relinerhaving properly sized and shaped annular orifices it.

The breech block and reliner orifices As here shown, the guns breechblock 2b is removably secured within the rear of chamber ii, andconstitutes only a partial closure therefor (see Figs. l--lZ-d-). Thisbreech block 20 is essentially cylindrical in shape. It is radiallyspaced from the inner wail of reliner I3 in a manner to form thesubstantially annular orice or venturi it that leads from the interiorof the gun chamber il, axially through the rim-like walls of thering-shaped reliner I3, and exits as four oblong openings in the rear ofthe gun, as shown in Figs. 1 and 4. A section of this annular orifics isshown at I5 in Fig. 3 wherein it may be seen that the breech block 20tapers inwardly from front to rear.

Four locking lugs shown at 2E in each of Fiss.

liner's interior wall.

1. 2 to 5B extend radially from this central b reech block 20 andthreadably interfit. as indicated at 22 in Figs. 1-2, .with the matingprotrusions 28 (again see Fiss. 1. 2 to 5B) on the re- When ythe threadson the periphery of locking lugs 26 are thus engaged with the threadso'f the mating protrusions 2i as just described, they securely lock thebreech block 20 within the rear of the reliner I3.

'Ihe chamber reliner's wall spaces which circumferentially separate thelocking protrusions 26 have a diameter larger than the maximum for thebreech lugs 28. This relationship enables free longitudinal movement bythose lugs through the spaces named. Such movement is utilized ininserting the breech block 28 within the reliner I3 and also inwithdrawing` the breech block therefrom, all ,in a manner presently tobe described.

As in the case of the pioneer Kroeger-Musser gun earlier identified.insertion and' locking ofthe breech block 2-within the chamber relinerI3 as shown in Figs. 1-2-3 constitutes a firm support for the ammunitionwhich it helps to position within` the weapon. The steel present in thebreech blocks central core structure is of sufficient thicknessandstrength to withstand, with appropriate factor of safety, the rearwardthrust exerted thereon during tiring,

The annular'orifice and recoil neutralization The '75 mm. recoillessfirearm illustrativeiy here shown edects recoil neutralization in theunique manner taught by the earlier mentioned copending applicationsSerial Nos. 536,590 and 577,830. In essence, the forces of rearwardreaction are neutralized by forwardly acting counterforces produced bythe rearward escape of gases generated by combustion of gunpowderthrough the earlier indicated annular orifice I5 (see Figs. 1--3-40between the guns breech block 2l) and the rear internal wall of chamberreliner lli wherein this breech block is secured.

It may appear from a rst impression of the drawings that the aforesaidannular oriiice It is a misnomer inasmuch as it incorporates a number ofsmaller orifices. However, there is a good reason for considering thefirearm to have but one annular orifice, principally because the nrearms recoilless mechanism actually functions as if there were only onesuch oriiice. To simplify understanding of the construction of thisannular orifice I t, a detailed description thereof follows.

As most clearly illustrated by Figs. 1 3-4- 55A, this annular orifice itis comprised of two distinct portions directly interconnected with eachother, both portions being included within the confines of the relinerI3. The maior portion of orifice it is distinctly annular, althoughirregular in form, and comprises the rearward dished-out portion ofreliner I3 (see Fig. 5A). When the breech block 2@ is in its closed butunlooked position, its central core fills the central area of thisrearward portion of annular orificeA It, leaving a circumferentialopening entirely surrounding the breech bloeit (see Figs. Iiv-). Thecontinuity of this portion of annular orifice I5 is broken only by therearward extensions of the reliner which terminate in the matingprotrusions 2b, and the four radial lugs 25 which engage withthoseprotrusions.

The minor portion of the annular orifice is actually divided up by four,supporting, axial walls of the reliner into four distinct axial openingswhich lead from the interior of gun chamber il rearwardly to merge withthe single annular opening above described.

When the breech block is in its closed and locked position (see Figs.'l-42-3) the described rearward portion of orifice Il loses its singleannular form and also becomes subdividedinto four separate orifices,axially continuous with the four openings just described above. In thiscondition. the gun is in its tiring position and, technically speaking.there are then four separate axial openings leading from the interior ofgun chamber Ii and exiting as four substantially oblong openings to therear of the gun as shown in Fig. l. However, I prefer to consider andwill hereinafter make reference to these separate axial venturi openingsas being all part of one annular orifice IB, for in actuality thesesubstantially identical openings all are directed toward a commonpurpose of applying a torque to the rearwardly escaping powder gases ata desired rate so as to counterbalance and neutralize the guns recoileffect. Y

Requirements of strength and other design principles necessitate the useof rearward reliner extensions which terminate in the mating protrusions2B. and the four radial lugs 25 which mate therewith, that have thesubstantial wall thicknesses illustrated by the drawings, Were it notfor such requirements my conception of a single annular orifice I5 wouldbe much more apparent. If it were possible suiiiciently to narrow thewall thicknesses of protrusions 28 and lugs 26, say to a few thousandthsof an inch. it would be considerably more apparent that annular orice i6may truly be considered to be of singular rather than of plural form.However. since that annular orifice or venturi, which in the drawingshereof is shown to be subdivided into a plurality of openings, actuallyfunctions as if it were one, I shall hereinafter make reference to it asii same were actually an uninterrupted whole. Y Y

Upon ignition of the propellant powder (not here shown) within cartridgecase 28 and the resultant forwardly discharge of the projectile 2l outof barrel I2, there is expelled through the perforations 30 of case 28combustionA gases which are projected radially against the surroundingchamber wall, and thence rearwardly out of the chamber through theannular orifice il now being described. By this acquiring momentumopposite to that of the forwardly'moving projectile the explosive gasesthus expelled set up counterforces which neutralize recoil.

In my improved 75 mm. weapon here shown this momentum eiIect issupplemented by making the forward. subdivided portions of the-gunsannular breech orice I5 oblong in a plane perpendicular to the guns axisand of the hourglass" shape parallel to the guns axis shown in Figs.1-3-4 to obtain the well-known Venturi action. Starting with arelatively broad radial width at its front or mouth end. the illustratedsubdivisions of the annular orifice `each gradually converges inwardlyto form a somewhat constricted throat portion; these annular oricesubdivisions then taperingly flare out from this throat region to theirrear exit as shown in Fig. 3. The well-curved entrance greatlyfacilitates funneling the rearward moving gases into the four annularorifice subdivision with a minimum o! wear thereon. while theillustrated exit angie is responsible for a satisfactory forward forcecomponent due to rapid expansion of the powder gases in passingrearwardly therethrough.

Acceptable performance is found to be achieved when the dimensions ofthe hourglass" orifice il have the relative proportions shown in Fig. 3.However. dimensions other than those shown may of course be utilizedwith varying degrees of relative effectiveness.

It will be noted that in my new design the major portion of the "venturiwinch serves to convergeescaping gases and thereby effect recoilneutralization is located within the replaceable reliner i3. Thisaffords important advantages over the earlier mentioned KroegerMusserweapons which were found to have certain portions of their chambers andbreech blocks highly eroded by action of the products of powderexplosion. In the here disclosed improved construction those portions ofthe gun chamber il and the breech block 20 are not exposed to the highlyerosive initial blasts of hot. high pressure gases. My invention hasovercome another trouble found with the earlier mentioned Kroeger-Musserweapons. In those prior art-weapons the gases which emerge past theconstricted throat portion of the annular orifice and which expand whilebeing discharged to the rear would also cause erosion of the gunchambers interior. Although f less damaging than the above mentionedinitial blasts of hot, high-pressure gases. the effect of theserearwardly expanding gases is definitely detrimental to the chamber.When my inventive reliner is employed, the chamber is entirely shieldedfrom those expanding gases as the venturi or annular orifice i5 throughwhich those gases pass is entirely situated within the replaceablereliner I3.

This elimination of such erosion as a factor detrimental to the chamberand breech is found to be substantially complete for all practicalpurposes, and consequently has increased the guns firing life span. Theunique "hourglass Venturi design further extends this period ofusefulness since the reduced wear which its internal wall undergoesminimizes the number of reliner replacements necessary to maintain thegun in good working order. This latter improvement was emphasized in theactual tests earlier mentioned wherein it was found that before onereliner wore out, an equivalent number of ammunition rounds could befired from my improved gun as could be fired in the entire lifetime ofthe longest lived prior art recoilless rifles such as are Wellrepresented by the '1 5 mm. weapon described in copending applicationSerial No. 577,830.

Adjustment for zero recoil As previously stated in the work which led tothe first successful recoilless type weapons it was found that forcomplete neutralization of recoil there exists an optimum ration betweenthe bore area ofthe guns barrel I2 and the throat area of the breechorifice i5. The factors which determine the value of this optimum ratiohave been more completely appraised in the earlier mentionedKroeger-Musser application Serial No. 536,590. This analysis indicatedthat the required bore-to-throat area ratio is dependent primarily Vuponthe amount of expansion obtained in the funnel I5, and to a lesserextent upon such factors as the relative weights of the powder andprojectile. f

In my improved firearm of the illustrative 'I5 mm. caliber heredisclosed this ratio for zero recoil is found to lie within the range ofabout 1.40

j to about 1.60. In the original Kroeger-Musser lo 'l5 mm. weapondesign, adjustment of this ratio to the optimum value which duringactualring does in fact produce zero recoil is provided by a special.adjustable breech orifice cone (54 oi' Ser. 577,830s drawings). Thiscone was intended to bear the brunt of attack by the powder gases, andto be replaced when it and the chamber were so worn as to alter theaforementioned ratio necessary for zero recoil.

Although effective in achieving its intended "adjusting" function, thetime and skill required to replace and adjust worn cones under combatconditions are handicaps to the guns usefulness. My reliner-equipped gunovercomes all these limitations as follows: On the average, one relinerwith the illustrated improved venturi will last as long as six old typecones as earlier explained with reference to Fig. 6, the need fortime-consuming replacements likewise being diminished; the reliner ismanufactured to specifications which include the predetermined optimumratio for practically zero recoil, and therefore needs no adjustmentswhen installed in the gun; andproper installation of my reliner is arelatively simple process of screwing it into place, whereas the priorart cones required somewhat skillful adjustment by means of a number oipositioning screws.

Experience, moreover, has shown that a reduction in annular orifice I5,which thereby increases the aforementioned bore-to-throat ration beyondthe optimum value for zero recoil, will cause a rearward kick todevelop. Likewise, enlargement of orice i causes a decrease in theboreto-throat ratio which, if diminished below the proper proportionrequired for zero recoil, will resuit in a forward kick of the weaponupon ring.

As the gun is used, the annular orice 'I5 will gradually become enlargeddue to erosion so that excessive forward recoil which eventuallydevelops will require the reliner i3 to be discarded. Since a certainamount of recoil can be tolerated without disturbing the gunner, it ispreferable at the outset to make the reliners orifice i5 somewhat underthe size required for zero recoil. Thus designed, the useful life of thereliner I3 may be further extended, for it may be used until such timeas the described annular orice enlargement causes excessive andintolerable forward recoil.

A clear understanding of this life-extending" design and other featuresmay be had by reference to the graph of Fig. 6. As there represented indotted line the prior art's recoil adjusting ring (54 of Ser. 577,830sdrawings) causes some rearward kick when new, but as erosion wears thering the breech orifice is thereby enlarged causing the gun to approacha zero recoil condition. A forward kick" then develops on further firingland increases toward the point where it would not be tolerable. Beforethis point is reached the worn ring must be replaced.

The solid line curve representing the kick imparted to my illustrative75 mm. reliner-improved weapon shows the comparatively more gradualchange from maximum backward to maximum forward recoil which enables onereliner i3 to last as long as six rings of the comparable prior art gun.This more gradual change, moreover, makes the variance in the smallamount of recoil that is present to be scarcely noticeable by the user,thereby making the gun easier to handle and control in combat ring.

Neutralization ofrotational reaction The principles regardingneutralization of rota- ,ifi tional reaction taught by co-pendingapplications Ser. Nos. 536,590 and 577,830 have again been adopted in myhere disclosed gun. Firearms having riiled barrels experience arotational reaction by virtue of the spinning motion that ring impartsto the projectile. In the particular gun here shown, barrel l2'sright-hand twist gives clockwise rotation (as viewed from the rear) toprojectile 21 upon forward movement thereof through the barrel. and thisright-hand acceleration of the proj ectiles mass impartscounterclockwise torque of equal magnitude to the barrel and chamber.

My improved 75 mm. weapon here shown includes provision for neutralizingsuch reactive torque by causing the explosive gases which rearwardlydischarge through the annular breech orifice i5 to impart to the weaponcounterbalancing torque of the same magnitude as that which the riedbarrel imparts to the projectile. This provision is eected by sospecially shaping the reliner protrusions 26 that the gases passingthrough orifice l5 have angular momentum imparted thereto.

Each of these reliner protrusions 2t has sidewalls that are slightly outof parallel with the guns axis. This sidewall arrangement (see\Figs. land 4) is such that the powder gases iiowing rearwardly through theorifice IE5 have imparted thereto a counterclockwise rotation (as viewedfrom the rear); these rearwardly moving gases being deflected to theright at the lower portion of the breech and to the left at the breechsupper portion.

By reason of the counteracting spin about the guns axis thus given tothe gases there is imparted to the chamber Ii a torque counteractingthat applied by the projectile. Only a relatively small degree ofangular twist (scarcely discernible in the drawings) is found sumcientto make the thus imparted torque of the same magnitude as the barrel i2imparts to the projectile 21 in advancing it through the riiled bore.

All neutralizing torque thus set up by the escaping gases is exerted onthe sides of the orice openings i5 and through chamber il is transmittedto the barrel l2. In this way the forces of rotational reactions 'areneutralized in a very simple yet highly effective manner.

Obviously, were the gun barrel to be ried with a left-hand twist,rotational reaction could be neutralized in exactly the same way merelyby shaping the reliner protrusions 25 in the opposite sense.

Breech block's withdrawal from chamber Explanation has already beengivenof how the breech block 2li is secured to the reliner I3 in the rear ofchamber Il by the aid of the breech blocks locking lugs 25 In theengaged position represented by Figs. 1-2-3 this support is all that isneeded to hold the breech block in place, and it is fully adequate torestrain the maximum chamber pressures which combustion of thepropellant charge (not shown) sets up.

To facilitate loading and removal of the cartridge case 28 after iring,there is provided mechanism (which is similar to that described incopending application Ser. No. 577,830) and which enables the breechblock 2B to be released and withdrawn from its chamber relinerattachment and to be swung to the downward position shown by Fig. 5B.During these actions the earlier mentioned breech bar 2l comes intoplay. To the two ends of this bar are amxed forwardly extendhandles, thebase of one of which is here intiicated in dotted outline at 23 inFig.l. I

The breech bar 2| is secured to the breech block 20 by means of fourbolts shown at 32 in Figs. 1 and 4. Intermediate this bar and the mainbody of the breech block is an oilset ring-like extension 33 of theearlier mentioned hinged breech block support member 23. 'Ihis supportmember is connected at its upper end with breech block 20's center andat its lower end is connected through a hinge pin 35 and an attachmentblock 36 to chamber iis lower side wail lThe hinge pin 35 has aconcavity in one side of its long axis llable by a portion of stud 3lvwhich thereby holds the pin in proper position within block 36 (seeFigs. 2-5-5A-5B) Both the breech block 20 and breech bar 2| may beturned around the ring extension 33 between the horizontal bar positionof Figs. 1-2--3 and the inclined bar" position of Figs. 4-5-5A-5B. Inthe gun here shown the range of this angular movement is of the order of45 degrees, as comparison of Figs. 1 and 4 will indicate.

Counterciockwise rotation of the weapons breech bar 2| serves to engagethe breech blocking lugs 25 into the mating threads of chamber relinerprotrusions 26 and thereby secures the breech block 2|! within thechamber reliner I3 as earlier explained (see Fig. 1); clockwise rotationmoves the locking lugs out of engagement with the reliner protrusionsand into the circumferential regions between protrusions. In the latterposition (see Fig. 4), the breech block 20 is free for rearwardwithdrawal from the chamber.

Once disengaged from chamber reiiner i3 as shown in Fig. 4. the breechblock 20 plus bar 2| and handles 29 are free to rearward withdrawal anddownward swinging around hinge pin 35 to the position represented byFig, 5B, When the breech block 20 is so withdrawn from chamber Il, theentire interior area of that chamber is unobstructed and prepared forready insertion of projectile 21 and cartridge case 28 into the gun, orready withdrawal of a fired cartridge case from the weapon.

To reinsert the breech block into the chamber. it is merely necessary toswing the breech block upwardly from the position shown in Fig. 5B; moveit forwardly into the chamber reliner I3s rearmost open end as indicatedby Figs. 5A and 5; and iinally give the handles 29 and bar 2| a turningmovement which brings the breech block locking lugs 25 to engage thereliners mating protrusions 26 as shown in Figs. 1-2.

The "open" breech lock and case extractor My improved weapon hereillustrated utilizes ltwo locking devices by which the breech block 20is respectively secured in the "horizontal bar" position of Figs. 1-2-3,and in .the "inclined bar" position of Figs. 4-5-5A and 5B. One of thesedevices will be spoken of as the cpen" brelch lock and the other as theclosed breech The open" breech lock and the case extractor arecooperatively combined, for all practical purposes. in one mechanism.The object of the open" breech lock, which will be discussed rst. is toprevent the breech block 20 and its attached bar 2| from being turnedout of the "inclined bar position at all times except when the breechblock is fully inserted into the guns chamber reliner I3. This lock thusserves to prevent the mating protrusions 26 from accidently striking thelocking lugs 25 when the breech block 20 is swung upward from the Figs.to the Fig. 5)

position. Once the breech block is in the Fig. 5 position, however. theopen lock is released and the bar 2| and breech block 20 may be turnedcounterclockwise from the Fig. 4 position to etiect the earlierdescribed locking register of the breech block with the matingprotrusions oi the reiiner as shown in Fig. 1.

'121e mechanisms utilized and their operation to eiect the caseextracting as well as the described locking actions will now bediscussed. Upon release of the closed" breech lock (later to beexplained in detail) the breech bar 2| and breech block 20 are turnedfrom the horizontal position of Fig. 1 to the inclined position of Fig.4. In so doing, a groove 38, cut in the breech block 20 tohave thecontour shown, is also moved from the position of Fig. 1 to .that ofFig. 4. A locking pin 39 projecting from the earlier mentioned extractori3 (see Rigs. 1, 2 to 5B) is held by spring 4| in constant register withgroove 38. As the breech block 23 is rotated from Fig. 1 to Fig. 4position, pin 33 is caused by groove 38 .to move radially inward fromits Figs. 1-2 position to the location shown by Figs. 4-5-5A-5B.

This radial movement of locking pin 39 is transmitted to the attachedextractor I3. As a result, the extractors sloping, pointed hook il! isbrought close to the inner margin of the breech block 20 (see Fig. 5)and, under pressure of the leaf (or a coil) spring 4| (see Figs. 2,55A-5B), is caused to ride radially along a ,bevelled groove 32 in thereliner I3 to engage the rim 43 o! cartridge case 28 and thereby extractsame (see Fig. 5A) as the breech block 20 is withdrawn from the chambertothe position of Fig. 5B.

When the breech block has been withdrawn somewhat beyond the position ofFig. 5A, the extractor hook 40 disengages itself from the cartridge caserim 43. 'I'his disengagement is brought about due to the fact that whilethe cartridge case 28 is being withdrawn rearwardly on an axial plane.the extractor hook 40 (being an integral part of breech bar 2|) isfollowing a radial path away from the axial plane by pivotinganticlockwise about the hinge pin 35. Upon such disengagement, pressureby leaf spring 4| pushes the extractor 3 against the breech block 20 asshown in Fig. 5B, and in so doing acts to lock the breech block 2liagainst rotation around the ring-like extension 33.

This locking is effected at the biocks edge which is in contact with theextractors inner point of bend as shown by Figs. 5-5A-5B. In alianmentwith extractor I8 when breech block 2B occupies the inclined barposition of Figs. 4 5 is a slot 45 (see Figs. 5-5A-5B) in the named edge(outer corner) of breech block 20. Once the breech block has beensuiilciently withdrawn from chamber I| .to tree extractor I9 fromcartridge case rim 33, spring 4I pushes the extractors inner bendportion into this slot 45 to eect the engagement shown by Fig. 5B. 'Iheextractor being anchored in slot 24 within the hinge i'ixture 23. thenamed engagement locks breech block 2 against rotational movement withrespect to fixture 23.

While in such open" position, the breech block 20 is thus non-rotativelymaintained at all times in readiness for reinsertion into the gunchamber (see Fig. 4) without interfering contact occurring betweenlocking lugs 25 and mating protrusions 26. Unlocking takes place by areversal of the foregoing procedure. When the hinge iixture 23, breechblock 20 and bar 2| are swung upwards from the Fig. B to theuFig. 5A andthen to the Fig. 5 posi-tions, the sloping edge or extractor hook itstrikes and rides radially outward against reliner I ts bevelled groovet2 (see Fig. 5). This withdraws the extractor from engagement with thebreech block 20's mating slot w, thereby freeing the breech block 20 andits attachments. By counterclockwise rotation of the bar 2l and breechblock 2t as aforesaid. the breech can now again be restored .to thehorizontal bar position oi' Figs. 1-2-3.

The "closed" breech lock The closed breech lock earlier mentioned nowbecomes effective to hold the breech block 2t in the horizontal barposition of Fig. 1 until after the gun's Bring action has taken place.This lock. along with the weapons ring mechanism, may satisfactorilyduplicate :the construction shown and described by co-pendingKroeger-Musser application Ser. No. 577,830.

Of the closed breech lock and the guns ring mechanism it need only herebe observed that the turning of breech bar 2 I to the horizontalposition oi Fig. l causes a spring loaded locking pin M 'which protrudesrearwardly ,from the breech block 2li to anove from its Fig. 4 locationto that of Fis. l thereby engaging a. slot ai (see Fig. 4) in the hingering 23. Such engagement locks the breech block 2li to the non-rotatablehinge-ring it, thereby preventing rotation of the breech block.

When the iiring mechanism (not here represented) is actuated (by meansnot here shown), the locking pin tti is simultaneously moved radiallyoutward from the Fig. l (locked) to the Fig. 4 (unlocked) position.Withdrawal of the breech block 20 from chamber II may then beaccomplished by clockwise turning the handles it and breech block abouthinge-ring 33, as previously explained, and then swinging the entireassemblage downwardly about hinge pin 35.

Loading and firing From the foregoing it will be seen that I haveprovided important life-increasing and other improvements to prior artrecoilless firearms Without impairing the advantages in connection withloading and ring possessed by those earlier weapons. To place theammunition round within my improved gun it is merely necessary to unlockbreech block 2li, withdraw it from the chamber reliner I3 and swing itdownwardly to the position shown by Fig. 5B, thus completely freeing therear opening into chamber Il.

The ammunition round 21-28 is now inserted into the opened chamber andthe rear of barrel lt's bore. the pre-engraved rotating band BI (seeFig. 2) of projectile 2B being placed into registry with the barrelsriings I6 (see Fig. 2). Forward thrust of the round is continued untilthe head rim di of cartridge case' 28 abuts with the reliner i3 as shownin Figs. 2--'5. In this position, the forward end ci? the cartridge caseis centered by the ride barrel and the cases head is similarly centeredwithin the chamber by the reliner I3 therearound. When the completeround is in the riile, the cartridge case 28 is indirectly supported bythe barrel I2 by virtue of the projectile located in the barrel which`communicates with the cartridge case. As the case is thus supported,there is a very slight annular space all around the forward end of thecase separating the case from the surrounding barrel. However, theinstant the projectile 4leaves the case the barrel then directly itsupports the forward end ci the cartridge casek so that this annularspace is interrupted.

The breech block 20 (together with bar 3| and handles 29) is now movedupwardly and forwardly into the chamber. In approaching and engagingwith the cartridge case head the i'iared recess in the breech blocksfront comes into abutment with the head and thereby restrains the caseagainst rearward movement. Counterclockwise rotation of the breech blockby bar 2i and handles 2@ in the manner earlier described, places the gunin readiness for ring, with the hammer (concealed in housing d8 of Figs.2-5-5A-5Bl in the necessary -cocked position.

By means oi' mechanisms similar to those utilized by the earliermentioned Kroeger-Musser firearms. but not here shown nor described, theweapon's safety catch is ilrst released. Then, by a pressure on atrigger button (not shown) situated in one ot the two bar handles 29 thehammer and firing pin are caused to detonate a percussion element andignite primer and propellant charges (also not shown) in the ammunitionround.

The resultant combustion of a propellant charge, discharge of theprojectile 2l, eHect and disposition of the cartridge case 2G andexplosive gases are also all amply described by co-pending applicationSer. No. 577.830; the operative principles there disclosed apply to myhereindiscloaed weapon as well.

After iiring, the subsequent withdrawal or the fired cartridge case fromthe chamber is preceded by first unlocking the breech block and thenwithdrawing that breech block rearwardly and downwardly out of registerwith the chamber reliner and into the position on hinge support 23 whichFig. 5B shows. Extraction of the red case in the manner previouslydescribed now becomes possible.

Other advantages of new construction From the foregoing description andaccompanying illustrations, certain mechanical details of my weaponwhich make possible the attainment of a number or earlier enumeratedobjects will have become evident. For example, the extractor I9 alwaysremains within the reliner Its recess I3 (see Figs. 2, 5-5A) where it iscompletely removed from the path of rearwardly moving explosive gases.This feature corrects a condition which led to rapid extractor erosionin the earlier Kroeger-Musser recoilless ries. Now shielded behind theprotecting reliner I3, the ex` tractor I9 in my improved gun survivesmany times longer than its counterpart in the earlier r design.

As previously mentioned, too, the removable reliner I3 bearing theportions of the annular oriiice I5 most subject to gaseous erosion maybe readily replaced. Such reliner renewal may satisfactorily befacilitated by a special wrench (not shown). The procedure used is toclamp the gun chamber il securely in a vise (not shown), remove stud 31out of contact with reliner I3, and then fasten the opposing jaws .ofthis named wrench onto the reliner through opposite ven-y turis i5 atthe rear of the gun with the breech block 2li and bar 2l in the Fig. 5Bposition. A counterclockwise turning of this wrench removes the relinerI3 from its threaded attachments M (see Figs. 2-3-5-5A-5B) to chamberil.

Thus, in only a few moments, the used reliner, l

having borne the brunt of attack by the powder gases, may be replaced bya new reliner I3. The

speed and ease with which this simple change can be made by the user ator near theeld of combat is a further advantage to this 81mlifeextending feature.

Summary The foregoing description has shown that my here disclosedimprovements have greatly enhanced the military value and usefulness ofthe open breech recoilless firearms now so widely acclaimed by theUnited States armed forces.

It will now therefore be apparent that I have improved the design andextended the usefulbreech designs which are peculiarly adapted to 75 mm.and other high caliber weapons and which eliminate the problem oi recoiladjustment; that I have protected the guns extractor mechanism fromerosion by the backward blast of escaping gases; and that I haveattained the foregoing improvements without sacricingthe advantages oflight weight, ruggedness and simplicity of action.

My inventive improvements, here exemplified as applied to a '75 mm.weapon, are capable of wide application and hence are not to berestricted to that specific form here used for purposes of illustration.

I claim:

1. In a recoilless nrearm, the combination of a barrel, a chambercommunicating with said barrel and having a rear diameter substantiallylarger than that of the barrels bore. an ammunition round comprising aprojectile positioned in the rear of said bore and a cylindricalcartridge case having a multi perforated metal wall in communication atits fox-ward end with said projectile and being of substantially smallerdiameter than the rear portion of said chamber, a rim extending radiallyfrom the rear portion of said cartridge case, a ring-like relinerremovably fixed by its outer periphery within said chambers rear portionand having spaced Venturi-like openings extending axially therethroughto form a substantially annular orifice leading from the chambersinterior through the reliner and to the rear exterior of the chamber andfurther having a concentric inner periphery whose rearward portion isthreaded and whose forward portion is diametrally reduced to encirclesaid cartridge case immediately ahead of its said rear rim whereby torestrain the case against forward movement and to support same inradially spaced relation to the chamber walls, and a breech blocksecured in said reliners rear threaded portion immediately behind saidcartridge case rim and also in radially spaced relation to the reliner'swalls therearound whereby to restrain the cartridge caso againstrearward movement and to form a continuation of the inner wall of thesubstantially annular orifice which leads to the rear exterior of thechamber.

2. In a non-recoil gun, the combination of a barrel, a chambervcommunicating with said bar- -.rel -and having a rear diametersubstantially larger than that of the barrels bore, an ammunition roundcomprising a projectile positioned in the rear of said barrel and aperforated cartridge case within said chamber communicating -with saidprojectile and having a cross sectional area substantially less thanthat of said chamber's Irear portion and being supportable at its frontby said barrel, a ring-like reliner removably fixed within the cham-bersrear portion so that its forward portion is in encircling relation tosaid cartridge case whereby to support same against lateral movement,said reliner being provided with a number of spaced Venturi-likeopenings which extend axially therethrough to form a substantiallyannular orifice leading from the chamber's interior to the rear exteriorthereof, and a breech block secured in spaced relation to the rearinterior of said reliner whereby to support said cartridge case againstrearward movement while at the same time continuing said annular orificewithout obstruction in conjunction with -said rellnrs rear interior.

3. In a recoilless firearm, the combination of a barrel, a chamberextending rearwardly from said barrel and having walls which taperoutwardly from the diameter of said barrels bore at the chambers frontto a substantially larger diameter at the chamber's rear, an ammunitionround comprising a projectile in the rear of said barrel and a cartridgecase containing propellant powder positioned within said chamber andcommunicating with said projectile, a metal wall for said case formingfor said powder a cylindrical enclosure of diameter approximately thesame as said surrounding chamber's forward end but substantially lessthan that chambers rear portion and being perforated by a relativelylarge number of openings distributed throughout the circumference andlength thereof. means including a removable ring structure lining theinside rear portion of said chamber for supporting said cartridge caseagainst lateral and forward movement and having axially extendingtherethrough Venturi-like openings which provide a substantially annularorifice leading from the chamber's interior to the rear exteriorthereof, and means including a breech block which continues said annularorifice without obstruction in the rear of said chamber and whichsupports said cartridge case against rearward movement and in spacedrelation to said chamber walls therearound, all said elements in theaforesaid combination so cooperating that upon igniting said powder thesaid projectile is discharged forwardly out of said barrel and at thesame time the powder combustion gases which result from such ignitionare expelled through said case wall openings radially into said taperedchamber and thence rearwardly out of said annular orifice to neutralizethe forces of recoil which tend to develop upon the forward firing of aprojectile from said firearm.

4'. In a recoilless firearm, the combination of a barrel, a chambercommunicating with said barrel, a removable ring structure lining theinside rear portion of said chamber and having spaced Venturi-likeopenings extending axially therethrough to provide a substantiallyannular orifice leading from the chamber's interior to the rear exteriorthereof, a breech block movable into and out of the rear interior ofsaid ring and having its periphery cut away at spaced portionscircumferentially of the block to provide interrupted locking lugs thatextend substantially radially from the central portion of the block,coacting protrusions from said rlngs inner wall engageable anddisengageable by said locking lugs upon locking and unlocking rotationof the breech block within the ring, a support for said breech blockailixed to the rear exterior of said chamber andasse i? in radialalignment with one of said rings protrusions, and a hinge memberextending radially from said support to the breech block inline with oneof said lugs in the breech blocks locked position and supporting thebreech block for rotative movement within the ring-lined chamber andalso for complete withdrawal therefrom as well as for imparting supportto the breech block when so withdrawn and also for guiding action forreinsertion into the chamber.

5. lin a firearm, the combination of a barrel, a chamber communicatingsaid said barrel and having a rear diameter substantially larger thanthat of the barrels bore, a cartridge case containing powder situatedwithin said chamber supportable at its front by said barrel and havingits wall so perforated that gases of powder combustion therefrom willexpand radially and further having a cross sectional area substantiallyless than that oi said charnbers rear portion so that the gases willhave room to expand, a .rien extending radially from the rear portion ofsaid cartridge case, a removable ring structure lining the inside ofsaid chambers rear portion and encircling said cartridge caseimmediately ahead of its said rear rim whereby to support said case inradially spaced relation to the rear chamber walls, a breech blocs;movable into and out of the rearward portion of said chamber-lining ringirn'xnediately behind said cartridge case and being secured therein whenrotated to a locked position and freed for Withdrawal therefrom whenrotated to an unlocked position, a, support member for said breech blockhingedly attached to the rear exterior of said chamber and extendingradially into pivotal juncture with the center of said breech blockwhereby the breech block is supported for rotative movement between saidlocked and unlocked positions and for withdrawal from and entry into thechamber, and an extractor nxture protruding from the forward face ofsaid support member for latching engagement over the rear rim of saidcartridge case upon withn drawal of the breech block from the chamber tothereby partially withdraw the cartridge case from the firearm at thesame time.

6. In a rearm, the combination of a barrel, a chamber communicating withsaid barrel, a removable ring structure lining the inside rear portionof said chamber and having a recess axially extending into the rearthereof, a cartridge case having a rear rim and containing powdersituated within said chamber supporta-ble at its front by said barreland at its rear by said ring structure and having its wall so perforatedthat gases of powder combustion will expand radially and further havinga cross-sectional area. substantially less than that of said chambersrear portion so that the gases will have room to expand, a, breech blockmovable into and out of the rearward portion of said ring and beingsecured therein when rotated to a locked position and freed forwithdrawal therefrom when rotated to an unlocked position. alongitudinal support member for said breech block having two surfaceswhich respectively face forwardly and rearwardly when said supportmember supports the breech block within said ring and further having twoextremities one of which is hingedly attached to the rear exterior ofsaid chamber in alignment with said ring-structure recess and the otherof which extends radially into pivotal juncture with the center of saidbreech blocks rear surface whereby the breech block is supported forrotative movement between said locked and unlocked positions and forwthdrawal from and entry into the chamber, an operating member aihxed tosaid breech block for transmitting turning and withdrawing and insertingmovements thereto, and an extractor fxture having an arm terminating ina hook protruding resiliently from the forwardly facing surface of saidsupport member into said ring-structure recess for latching engagementby the hook with said cartridge cases rear rim upon withdrawal oi thebreech block from the ringlined chamber to simultaneously therebypartially withdraw the cartridge case from the iireerm, said extractorarm then being projected into locking engagement with said breech blockwhere it prevents rotation of the breech block out of unlocked positionuntil such time as the breech block has again been fuily reinserted intothe chamber when said extractor arm is removed from said lockingengagement in the breech bloei; to said recess in the chamber-liningring upon contacting said ring.

'7. In a non-recoil gun, the combination oi a barrel, a chambercommunicating with said barrel, a ring-like reliner removably xed withinthe chambers rear portion and having spaced Venturi-llke openingsextending axially therethrough to form a substantially annular oriiiceleading from the chambers interior to the rear exterior thereof, saidreliner having between two of its Venturi openings a recess axiallyextending into the rear of the reliner, a breech block movable into andout of the rear interior of said reliner and being secured therein whenrotated to a locked position and freed for withdrawal therefrom whenrotated to an unlocked position, a longitudinal support member for saidbreech block having two surfaces which respectively face forwardly andrearwardly when said support member supports the breech block withinsaid ringlike reliner and further having two extremities one of which ishingedly attached to the rear exterior of said chamber inalignment withsaid ring's recess and the other of which extends radially into pivotaljuncture with the center of said breech block's rear surface whereby thebreech block is supported for rotative movement between said locked andunlocked positions and for withdrawal from an entry into the chamber. anoperating member ailxed to said breech block for transmitting turningand withdrawing and inserting movements thereto. and an extractor xtureprotruding resiliently from the forwardly facing surface of said supportmember and aligned to rest within said reliners recess when the breechblock is inserted into the chamber whereby to be shielded from gaseouserosion during firing.

CLARENCE WALTON MUSSER.

